The present invention is related to the field of virtual magnetic tape storage devices and method of operation.
In typical magnetic tape storage environments, many tape cartridges, tape drives, and library devices are distributed among various clients. These clients may be single user workstations, work groups, departmental servers, or large multi-user platforms. The management complexity of these environments increases as a function of how much data is stored and the heterogeneity of the computational environment. Storage management costs are a significant portion of the information technology budget, particularly in emerging markets, such as those known as open systems. Open systems shops are those that are based upon network operating systems such as UNIX, NT servers, and the like.
In open system markets, the primary use of magnetic tape technology has been concerning data security, particularly for data backup, restoration and disaster recovery. A combination of factors has hindered the adoption of magnetic tape for other applications. One of these factors is management complexity. While automated tape libraries and hierarchical storage tape systems provide a low-cost solution for storing vast amounts of data, they involve a reasonable amount of management complexity.
There has been a general tension between client needs and system management needs, especially in tape applications. For example, when library and tape device resources are centrally located, clients often need to contend with resource partitioning schemes that are by definition a sub-optimized utilization of resources. An example here is the need to maintain individual scratch tape pools for each partition. Alternatively, client usage of centralized resources may be scheduled with each client using a common pool of resources in turn. This is a challenge in environments characterized by growing information technology resource needs and periodic workloads, and aggravated by poor communications between centralized resources management and the clients. Virtual tape technology often makes the situation more challenging. For example, when a client wishes to backup a data set for export to another physical site, the mismatch between the multitude of virtual tape labels and their real counterparts can introduce errors in the recovery process.
Several technologies, such as virtual magnetic tape, storage area networking, and centralized systems management tools have evolved over the years to address data storage management challenges. Each of these technologies has addressed certain portions of the management problem. For example, virtual tape technology has enabled tape buffering and data transfer rate matching to achieve highly efficient utilization of the tape drives. Storage area networks have eliminated the bulk of the problems related to co-location of storage devices and clients, allowing open systems to centrally locate and manage storage resources. Finally, systems management tools have promised to provide common tools for data management in diverse environments.
Each of these technologies, however, solves only some problems. For example, virtual tape volumes are often designed to emulate real tape cartridges. From the client""s point of view, there is no management advantage to use the virtual tape volumes over real tape cartridges. The client still must know on which virtual tape volume the desired data is stored, and the client must provide control of the storage appliance to mount and dismount the virtual tape volumes. In another example, system management tools tend not to provide uniform support for all data storage systems. Client provided management of a storage appliance provided from one vendor is usually incompatible is some respect with a second storage appliance provided from another vendor.
To improve client acceptance of magnetic tape as the preferred media for their applications, a tape storage system is required that is simple to use and is available at all times. Ideally, the tape storage system would appear to the client as one tape cartridge always mounted in a dedicated tape drive connected directly to the back of the client""s computer, yet realize the benefits of centralized management. Capacity of this tape cartridge should be variable to meet the client""s requirements and budget. The upper bound of the capacity should be virtually limitless for high end clients.
The present invention is a system that emulates a tape cartridge mounted in a tape drive, and a method of managing the system. Communication between the emulated tape drive and a client is performed using an interface protocol. An addressable range of the emulated tape cartridge matches or exceeds the addressable range defined in the interface protocol giving the tape cartridge the appearance of a practically limitless capacity. In operation, one or more storage appliances provide the emulation of the tape drive and multiple virtual tape volumes. An interface manager control mounting of the multiple virtual tape volumes in the tape drive so that they appear as one large tape cartridge to the client.
The interface manager includes an address map function that maps the interface protocol defined addresses into the various virtual addresses used by the multiple virtual tape volumes. In an alternative embodiment, address mapping can be used to preserve existing blocks of data by mapping new data to unused blocks elsewhere in the tape cartridge instead of overwriting the existing data. In a second alternative embodiment, the interface manager may include a protocol converter that translates between the interface protocol used to communicate with the client, and a second protocol used to communicate with the storage appliance. A third embodiment includes a policy controller that sets one or more performance parameters for the emulated tape drive or tape cartridge based upon the client""s level of service.
Accordingly, it is an object of the present invention to provide a system and method that emulate a tape cartridge mounted in a tape drive, wherein a client communicates to the emulated tape drive through an interface protocol, and the tape cartridge""s capacity matches or exceeds the addressable range defined by the interface protocol.
These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings.